1. Field
The present invention relates to a vane pump device.
2. Description of Related Art
For example, a vane pump disclosed in JP-A-2013-50067 includes a main discharge port on a high discharge pressure side on which a discharge pressure is high, and a sub discharge port on a low discharge pressure side on which a discharge pressure is low. In this vane pump, two arc-shaped high-pressure oil introduction ports, which introduce high discharge pressure oil of a high pressure chamber to bottom portion side spaces of a portion of vane grooves in a circumferential direction of a rotor, are provided around a center hole of an inner plate so as to face each other on the same diameter of the inner plate. An annular back pressure groove is provided in a surface of an outer plate which is adjacent to the other surface of the rotor, and communicates with bottom portion side spaces of all of the vane grooves of the rotor, and with the high pressure chamber via the high-pressure oil introduction ports of the inner plate. The high-pressure oil introduction ports of the inner plates, communication grooves, and the back pressure groove of the outer plate are set to communicate with the bottom portion side spaces of the vane grooves at any rotational position in a rotation direction of the rotor. Accordingly, during rotation of the rotor, high discharge pressure oil discharged from the discharge port is supplied to the annular back pressure groove of the outer plate via the high-pressure oil introduction ports of the inner plate and then the bottom portion side spaces of a portion of the vane grooves of the rotor, which communicate with the high-pressure oil introduction ports. At the same time the high discharge pressure oil is supplied to the annular back pressure groove of the outer plate, the high discharge pressure oil is introduced to the bottom portion side spaces of all of the vane grooves of the rotor which communicate with the back pressure groove, and the tips of vanes are pushed against and brought into contact with an inner circumferential cam surface of a cam ring by the pressure of the high discharge pressure oil introduced to the bottom portion side spaces of the vane grooves.
JP-A-2011-196302 discloses a vane pump including a switching valve that switches between a full discharge position at which a working fluid is suctioned and discharged in both main and sub regions and a half-discharge position at which the working fluid is suctioned and discharged only in the main region. The switching valve switches the pressure of the working fluid introduced to vanes in the sub region such that the vanes retract to the rotor and move away from the inner circumferential cam surface of the cam ring at the half-discharge position.
In a configuration in which the annular back pressure groove is provided to communicate with the bottom portion side spaces of all of the vane grooves of the rotor and the high pressure chamber, and high discharge pressure oil is introduced to the bottom portion side spaces of the vane grooves via the back pressure groove, the following problems may occur. That is, high discharge pressure oil is introduced to the bottom portion side spaces of the vane grooves, and the hydraulic pressure of a pump chamber on the low discharge pressure side is lower than that of the pump chamber on the high discharge pressure side. As a result, pressure pushing the tips of the vanes against the inner circumferential cam surface of the cam ring is increased, and torque required to drive rotation of the pump is increased.